Centrifugal separator



Jan. 11, 1966 K. E. TOPPING CENTRIFUGAL SEPARATOR 2 Sheets-Sheet 1Original Filed Jan. 11. 1961 Jam 1965 K. E. TOIPPING GENTRIFUGALSEPARATOR 2 Sheets-Sheet 2 Original Filed Jan. 11, 1961 Unite Statesfiatetit G 3,228,593 I CENTRIFUGAL SEPARATQR Kenneth E. Topping,Foxboro, Mass, aasignor to Bird Machine (Iornpany, South Walpole, Mass,a corporation of Massachusetts Continuation of application Ser. No.82,044, Jan. 11, 1961.

This application Dec. 3, 1964, Ser. No. 418,582 2 Claims. (Cl. 233-7)This application is a continuation of application Ser. No. 82,044, filedJanuary 11, 1961, now abandoned.

This invention relates to centrifugal separators, and more particularlyto such separators of the continuous solid bowl type wherein a helicalconveyor, rotated at a differential speed from that of the bowl,progressively moves solids concentrated adjacent the bowl wall bycentrifugal force toward the discharge end of the bowl, usually smallerthan the entrance end.

With centrifugal separators of the type concerned, difficulties ofchoking have been encountered with'certain material such as coalfines'due to bridging of solids between the conveyor and the bowl,locking the two against relative motion, thus causing strain and evenbreakage in the operating gearing, and requiring dismantling andcleaning of the machine before it can again be placed in effectiveoperation. In Milliken et al. Patent No. 2,600,372, issued June 10,1952, there is disclosed a solution to this problem according to whichthe inner bowl surface is provided with raised strips which act toanchor a bed of solids to thevinner surface of the bowl. Thisarrangement, in combination with a smooth surfaced conveyor, was foundto operate satisfactorily and without choking on coal fines and othermaterials with which a choking problem had theretofore been encountered.

In machines according to the aforesaid patent wherein the inner surfaceof the bowl is of ordinary iron or steel construction, the bed of solidparticles initially formed between'the strips tends to remain intact andto provide the working surface of the bowl over which the subsequentlycentrifuged solids are'worked by the conveyor to the discharge end ofthe bowl. Prior to the present invention it was found that the operationof such machines upon soft, non-abrasive solids could be improved byforrning the bowl and strips of stainless steel with the surfacesthereof exposed within the bowl polished to a very smooth state. Withthis arrangement the solids bed was forced by the conveyor to slip onthe polished surface toward and out of the discharge end along with thesolids above the bed, the bed being constantly replenished by incomingcentrifuged solids, and continuing to prevent clogging by means of thebowl strips in the same manner as the stationary bed. Machines somodified have been operated successfully on non-abrasive materials suchas polyvinylchloride and other similar resins to provide increasedcapacity, greater separation efliciency and a better product than isobtained with the permanent bed machine.

The present invention resulted from efforts to obtain similarimprovement with centrifuges operating on slurries of hard, abrasivesolids. Due to the different character of the solids, it did not followthat by smoothing the bowl surface the sliding bed action which hadproduced improved results with soft-solid slurries" would be obtainablewith hard, abrasive solids. Even if such action could be obtained, itsutilization in processing. abrasive particle slurries appearedimpractical because of the problem of bowl wear. Continued rubbingcontac't of such particles with a surface even as hard as stainlesssteel produces rapid wear. In the centrifugingof; coal fine slurries,for example, in apparatus according'to the above patents, it has beenfound that the conveyor is worn by the abrasive solids at such a rate asto require repair or renewal after the processing of the order of onehundred thousand tons of the coal or, at the usual operatingrate offifty tons per hour, about two thousandhoursof operation. from wear bythe bed of solids permanently anchored thereto, but if this weretransformedinto a sliding bed on a polished stainless steel bowl thewear rate on'the bowl would be high. Such wear would be expected eitherto prevent the sliding action, due toroughening of the bowl, or towearout the bowl at an uneconomically rapid rate.

As a possible means of overcoming the wear problem, it was conceivedthat the requisite hard smooth inner bowl surface and strips might beprovided as a relatively thin, smooth stainless steel liner within thebowl'and removably attached thereto. If such a liner would'function toproduce the sliding bed action it could be replaced when worn atafraction of the cost of replacing a bowl, and consequently might makethe operation economical.

Such a linerwas initially tried in the bowl of a centrifugeoperating onabrasive potash'slurries of finer'particle' size range than coal fines.In previous operation on th e same slurries the bowl had strips andordinary unsrnooth inner bowl surface producing the bed-anchoring effectdescribedin the patent mentioned above. When'first'started, thesmooth-surfaced liner and strips produced animproved operationcharacteristics of the sliding bed' effect that had been previouslyobtained with soft solid slurries. But' the effect was temporary andafter a very short period of operation the machine lost all improvementand reverted to its former capacity, efficiency and product quality, itbeing obvious that the machine Wasoperating' with an anchored bed asbefore. Continued operation produced no change or improvement anddid notappreciably wear the liner as it would have done with sliding bedaction. I

Despite this failure, it was decided to try another liner, this time ina centrifuge that had been operatingon coal fines with a solids bedpermanently anchored in the stripped bowl. capacity, efficiency andproduct was obtained and maintained. The previous normal production rateof'50 tons per hour was raisedto 67 tons per hour while the conveyingloads measured at the gear unit dropped from 430 pounds to only 300pounds and the product degradation was substantially reduced dueapparently to reduced shear. After this greatly improved operation hadbeen maintained substantially unchanged for 600 hours, the

been installed in other machines operating on coal fines with the sameimproved results. These tests clearly indi- In that apparatus, the bowlwas protected This time a remarkable improvement'in cate that theimproved operation can be maintained even beyond the previous100,000-ton limit for conveyor renewal because of the reduced wear onthe conveyor and because the apparent wear rate on the liner was notgreat enough to call for liner replacement at that tonnage. In anyevent, the improvement was so substantial as to make use of the lineradvantageous even if the liner lifewere substantially less than 100,000tons processing.

Although this has not as yet been definitely proved, it is believed thatthe initial failure on potash was due to a lack of proper strip heightand conveyor clearance in relation to slurry particle size range. In thepotash machine, the height of the strips was inch and the clearance ofthe conveyor from the strips was inch and from the'liner surface, inch.Since the maximum particle size (greatest diameteryof the potash slurrywas less than inch, the bed formed between the strips was more than sixtimes the maximum particle size and the clearance of the conveyor overthat was greater than the maximum particle size. In the initial liner.tested on coal fines the strip height was- /2 inch but this was onlytwice the maximum particle size of M4 inch. The clearance of theconveyor from the strips was /s inch or only one-half the maximumparticle size. Apparently, the clearances in the potash machine werejust at the maximum limit at which the conveyor was able to slide thesolids bed, so that after only slight wear the limit was exceeded andthe action was lost. r

In accordance wit-h the foregoing, the object of this invention is toprovide a centrifuge of the type concerned having the above and othernovel features of construction, which enable it to process slurries ofabrasive particles without choking more efliciently and at less cost jFIG. 1 is a view partially in side elevation and partially inlongitudinal vertical cross section of one form of the apparatus;

FIG. 2 is a partial side elevation and partial vertical cross sectionview of the bowl of the apparatus of FIG. 1;

FIG. 3 is a front (right hand) end view of the bowl of FIG. 2;

FIGS. 4 and 5 are fragmentary detail section views on the lines 4-4 and5'5 respectively of FIG. 2;

FIG. 6 is a fragmentaryasection view of a bowl embodying a modifiedconstruction.

Referring now to the drawings, and first to FIG. 1, the machine as shownhas a pair of supporting standards 10 and 12 upon which are fixedlymounted bearing collars,

14 and 16 respectively. Within the bearing collar 16 is rotatablyjournaled the drive sleeve 18 of the centrifuge bowl designatedgenerally at 20, the sleeve 18 being fast at one end to a flange boltedto the bowl to form one end wall 22 thereof. A belt drive sheave 24driven from a motor (not shown) is fixedly connectedto the outer end ofdrive sleeve '18.

Fixed to the opposite, or left hand, end wall 26 of the bowl, is adriven sleeve 28 'rotatably journaled within bearing sleeve 14, andoperably connected at its outer end to a reduction gear unit 30 mountedwithin -a casing 32 fixed to the collar 14. A stub shaft 34 driventhrough the reduction gear unit has fixedly attached thereto the convvveyo r drive shaft 36 which isrotatably journaled within the drivensleeve 28.

The conveyor comprises a hollow casing 38 ,forrned of one large and onesmall diameter cylinderjoinedtogether, on the outer surface of which issupported the a feed pipe 52 which extends loosely through the sleeve 46and end wall 44 of the casing 38 so that the conveyor and bowl arerotatable with respect to the pipe. A wall 54 fixed to the casing 38 isopposite the inner end of the feed pipe and acts to define a feedchamber into which the incoming slurry is discharged through pipeopening 55 and from which it is discharged into the bowl through outlets56.

A stationary outer casing 58 of the centrifuge is fixedly connected ateach end to the supports 10 and 12 by means of end walls 60 and 62through which the sleeves 18 and 28 are rotatably journaled. An annularbaffle 64 adjacent the left hand end of casing 58 cooperates with anannular lug 66 on the bowl to form a solids discharge chamber, intowhich the solids progressed to the smaller end of the bowl aredischarged through ports 70 and from which they are removed through aconnecting flue 72. An annular flange 74 within the opposite end ofcasing 58 cooperates with the end wall 22 of the bowl to form a liquidreceiving chamber'76 from which the liquid component is withdrawnthrough pipe connections (not shown). The liquid is discharged intochamber 76 through openings in end wall 22 over anadjustable rim or dam78.

In operation of the machine as sofar described, the bowl is driventhrough drive sheave 24 and sleeve 18 in one direction at apredetermined rate sufficient to provide the requisite centrifugalforce, and the conveyor is driven therefrom through sleeve 28, thereduction gear unit and shaft 36 in the same direction but at adifferent rate to produce the required differential motion between thebowl and the conveyor. The solids from the incoming slurry whichtend toseparate from the liquid toward the bowl due to centrifugal force areconveyed to the left by the conveyor and into the solids receivingchamber 68, while the liquid component overflows the dam 7 8 into thecompartment 76.

As so far described, the machine is substantially the same as disclosedin the aforesaid Patent No. 2,600,372. Turning now to the improvementswhich the present invention provides in the bowl and its relation to theconveyor, it will be seen that the bowl as shown in FIGS. l-S has acylindrical front section followed by two successive frusto-conicalsections of diiferent cone angle, with the smaller angle cone formingthe discharge end. This particular shape is notessential for purposes ofthe present invention, although it is preferred that the discharge endhe of smaller diameter than the entrance end of the bowl. The front bowlsection may also be frustoconical or the entire bowl may be of a singlefrustoconical section,as in the FIG. 5 embodiment of theaforesaidpatent.

Asshown in FIGS. 1-5, the bowl has an outer wall 80 of suitable metalsuch as cast iron or steel, conveniently formed in three sections joinedtogether end to end by welding. Wall 80 is provided at four equallyspaced intervals about its axis with four rows of bolt holes forreceiving the shanks of bolts 82. Seated against the inner face of wall80'is a liner 84 of relatively thin, hard wearing and smooth surfacedmaterial, desirably of stainless steel and preferably of cold rolledstainless steel, as this material, particularly that formed with what isknown in the trade as a No. 2-B finish, has a polished finish formed inthe cold rolling which is exceedingly smooth and excellent for. purposesof the present invention. As in the:

case of the outer bowl wall 80, the liner may be conveniently formed inseparate sections joined end to end by butt welding as shown in FIGS. 4and 5, the weld preferably having the convex form shown at 86 in FIG. 4*to protect against wear.

. four rows of bolt holes to align with the bolt holes in the external.wall 80 and also to receive the shanks of bolts 82.

Upon the inner surface of 1 the liner are mounted by means of the bolts82 four sets-of strips 88 overlying Liner 84 is also provided With-- thebolt holes in the outer wall and lining and being provided withcountersunk, bolt holes 90 for receiving the inner ends of bolts 82.These strips are also of hard wearing, smooth surfaced material,preferably the same as that of the lining. As shown, the strips areformed of three separate sections, each conforming in length to one ofthe three bowl sections of difierent shape, although they may be formedof one piece bent to conform to the bowl contour.

In the construction shown, the strips may be removed from the liner andthe bowl by partially withdrawing the bolts 82. By further withdrawingthe bolts 82 the liner may be removed from the bowl through its largerend. This arrangement is preferred since it permits the strips to beremoved and replaced independently of the liner in the event they wearfaster than the liner, though this feature is not essential and thestrips may be permanently attached to, or formed integral with, theliner. However, it is essential that the liner be removable, and this ispreferably accomplished by bolting in the manner shown, which may beaided in security of fastening by readilyruptured tack welds of liner toouter wall at one or both ends.

Conveyor blade 40, also formed of hard wearing, smooth surfacedmaterial, is contoured to the bowl so that it has a uniform clearanceabove the strips and the inner surface of the liner. As above indicated,these clearances are important since, if they are too great,satisfactory sliding-bed action, which provides improved operationaccording to the invention, may not be obtained. In general, it ispreferable that the clearance of the conveyor above the strips be assmall as consistent with manufacturing tolerances, and may be of theorder of to 4; inch. Greater clearances may be provided, particularlywhere the machine is for processing slurries containing a substantialproportion of relatively large particles, such as coal fines, but it isdesirable that this clearance be less than, or at least notsubstantially exceed, the maximum particle size if that is possible.

The clearance of the conveyor from the inner surface of the liner is afunction of the thickness or height of the strips 88. Here also the mostdesirable clearance will depend to some extent on the nature of theslurry being processed. With large particle slurries such as coal fines,a strip thickness of /2 inch plus a conveyor clearance from strips of /sinch has been found satisfactory, although somewhat greater or lesserstrip thicknesses and clearances may be used. With smaller particleslurries the strip thickness, as well as the total clearance from theconveyor to the liner, may desirably be less. Desirably, the stripscorrespond in thickness to from about one to four times the largestparticle size present in significant quantity in the slurry beingprocessed, making the desired clearance from the liner about two to fivetimes such particle size.

The strips are desirably relatively narrow, about 1 inch width beingsuitable in bowls of 36 to 54-inch or larger diameters. The use of fourstrips, or set of strips, spaced at equal radial intervals is notessential. However, it has been found that the use of a greater orlesser number of strips tends to interfere undesirably with the slidingaction of the conveyor on the solids bed formed between each pair ofstrips.

Due to the decrease in diameter of the bowl toward the exit end, thestrips are closer together at that end than at the front end. This alsohas some tendency to interfere with the sliding bed action. Where suchdiameter difference is very substantial, it may be desirable to make thestrips wider toward the front end and narrower toward the discharge endto reduce this difference in spacing.

In the embodiment so far described, the strips and liner are providedthroughout the length of the conveyor. This is desirable but notessential. Most of the work of the conveyor is accomplished toward theexit end of 6. the bowl, so that the strips and liner may be omitted atthe front end, for example from the cylindrical section in FIG. 2. Theliner and strips should, however, extend from adjacent the discharge endfor a substantial part of the conveyor length.

FIG. 6 illustrates a modification in which the liner and strips areconfined in length to the effective working length of the conveyor, thisfigure also illustrating modifications in strip and bowl design. In FIG.6 the outer wall 96 of the bowl is made in two sections, a frontcylindrical section and a rearward frusto-conical section. Thecylindrical section is preferably made somewhat thicker than the otherwith the two sections joined so that the thicker cylindrical sectionprojects inwardly of the other. The liner 98 is coextensive in lengthonly with the frusto-conical section which is opposite the effectiveworking length of the conveyor. The inner end of the liner abuts theinwardly projecting end of the thicker cylindrical portion and issubstantially flush with the surface thereof.

The strips 100 of the FIG. 6 embodiment are also modified and instead ofbeing rectangular and arranged parallel to the bowl axis, they areformed as sections of a helix and the bolt holes 102 therein, as well'as the matching holes in the liner and outer wall are arranged in acorresponding helix. This helix or spiral desirably has a pitch whichapproximates the angle to the bowl axis at which the conveyor tends tomove the solids, which may be of the order of 30. This arrangementsomewhat reduces the friction of the sliding bed on the sides of thestrips, tending to reduce both strip wear and the conveyor load ascompared with the previously described embodiment.

Visual observation has shown that with the bowl and conveyor properlyconstructed and interrelated in accordance with the invention as abovedescribed, the abrasive solids form into beds between the strips, andthese beds are continually slid to and out of the exit end of the bowlby the conveyor. It is this action which is believed responsible for thegreatly improved results obtained as above described. When the strips orliner become sufficiently worn to warrant it, either or both may bereadily replaced with the construction shown and at insubstantial costconsidering the improved operation obtained.

It will be appreciated that there have been particularly shown anddescribed herein only preferred embodiments of the invention and thatchanges in the form and detail thereof may be made within the spirit andscope of the invention.

What is claimed is:

1. In a centrifuge for separating solid, abrasive particles from liquidwhich includes a rotatable bowl adapted to receive the fluid-solidsmixture, a solids discharge chamber adjacent one end of the bowl, aliquid discharge outlet, a rotatable, helical conveyor coaxially mountedwithin the bowl, and means for rotating the bowl and conveyor atdifierential speeds so that the solids are concentrated against the bowlby centrifugal force and are progressed to the discharge chamber by theconveyor, the improvement which comprises the combination with the bowlof a liner mounted within the bowl and forming a continuous innerworking surface thereof surrounding its axis, said liner having atlea-st a portion thereof diminishing in diameter between its ends withthe smaller end contiguous to said solids discharge chamber, said linerbeing of hard wearing, smooth surfaced material at least substantiallyas hard wearing and smooth surfaced as cold rolled stainless steel andbeing provided on its inner surface with a plurality of radially spaced,generally parallel raised strips extending longitudinally of the bowlaxis substantially the full length of said liner portion, said stripsbeing of such low number and relatively narrow width as to expose themajor portion of the inner surface of the liner between them, theclearance 7 of the conveyor from the liner being of the order of two tofive times the diameter of the largest particles present in significantquantity in the mixture to be processed,

said clearance of the conveyor from said strips not substantiallyexceeding said diameter, whereby to enable the conveyor to continuouslypush said beds over the smooth surface of the liner and from the exitend thereof and to maintain sai-d action despite substantial wearproduced thereby on said liner and strips, and means removably attachingthe liner to the bowl to permit removal and replacement thereof whenrequired by wear.

2. A combination according to claim 1 wherein said 8 strips are oftheorder of four 'in number andof one inch in width.

References Cited by the Examiner UNITED STATES PATENTS 1,064,184 6/1913Wels 233 7 2,600,372 6/1952 Milliken 61 al. 233*? 3,096,282 7/1963Trotter 233 '7 10 M. 'CARY'NELSOVN, Primary Examiner.

H. K'LINKSIEK, Assistant Examiner.

1. IN A CENTRIFUGE FOR SEPARATING SOLID, ABRASIVE PARTICLES FROM LIQUIDWHICH INCLUDES A ROTATABLE BOWL ADAPTED TO RECEIVE THE FLUID-SOLIDSMIXTURE, A SOLIDS DISCHARGE CHAMBER ADJACENT ONE END OF THE BOWL, ALIQUID DISCHARGE OUTLET, A ROTATABLE, HELICAL CONVEYOR COAXIALLY MOUNTEDWITHIN THE BOWL, AND MEANS FOR ROTATING THE BOWL AND CONVEYOR ATDIFFERENTIAL SPEEDS SO THAT THE SOLIDS ARE CONCENTRATED AGAINST THE BOWLBY CENTRIFUGAL FORCE AND ARE PROGRESSED TO THE DISCHARGE CHAMBER BY THECONVEYOR, THE IMPROVEMENT WHICH COMPRISES THE COMBINATION WITH THE BOWLOF A LINER MOUNTED WITHIN THE BOWL AND FORMING A CONTINUOUS INNERWORKING SURFACE THEREOF SURROUNDING ITS AXIS, SAID LINER HAVING AT LEASTA PORTION THEREOF DIMINISHING IN DIAMETER BETWEEN ITS ENDS WITH THESMALLER END CONTIGUOUS TO SAID SOLIDS DISCHARGE CHAMBER, SAID LINERBEING OF HARD WEARING, SMOOTH SURFACED MATERIAL AT LEAST SUBSTANTIALLYAS HARD WEARING AND SMOOTH SURFACED AS COLD ROLLED STAINLESS STEEL ANDBEING PROVIDED ON ITS INNER SURFACE WITH A PLURALITY OF RADIALLY SPACED,GENERALLY PARALLEL RAISED STRIPS EXTENDING LONGITUDINALLY OF THE BOWLAXIS SUBSTANTIALLY THE FULL LENGTH OF SAID LINER PORTION, SAID STRIPSBEING OF SUCH LOW NUMBER AND RELATIVELY NARROW WIDTH AS TO EXPOSE THEMAJOR PORTION OF THE INNER SURFACE OF THE LINER BETWEEN THEM, THECLEARANCE OF THE CONVEYOR FROM THE LINER BEING OF THE ORDER OF TWO TOFIVE TIMES THE DIAMETER OF THE LARGEST PARTICLES PRESENT IN SIGNIFICANTQUANTITY IN THE MIXTURE TO BE PROCESSED, SAID CLEARANCE OF THE CONVEYORFROM SAID STRIPS NOT SUBSTANTIALLY EXCEEDING SAID DIAMETER, WHEREBY TOENABLE THE CONVEYOR TO CONTINUOUSLY PUSH SAID BEDS OVER THE SMOOTHSURFACE OF THE LINER AND FROM THE EXIT END THEREOF AND TO MAINTAIN SAIDACTION DESPITE SUBSTANTIAL WEAR PRODUCED THEREBY ON SAID LINER ANDSTRIPS, AND MEANS REMOVABLY ATTACHING THE LINER TO THE BOWL TO PERMITREMOVAL AND REPLACEMENT THEREOF WHEN REQUIRED BY WEAR.